The invention relates to an improvement of a battery casing having a battery receiving chamber covered by a lid which forms part of an external wall of an instrument for which the battery provides a power supply.
A battery casing of the kind described is used in a number of high precision instruments such as photographic camera, exposure meter, quartz operated watch or the like which utilizes a small size battery, in particular, mercury or silver battery, as a power supply.
Referring to FIG. 1, there is shown a conventional battery casing which is adapted to contain battery 1 in its battery receiving chamber 2, which is formed by nonconductive casing frame 3 which is in turn disposed inside a photographic camera. Electrical terminal member 4 is disposed on the bottom of chamber 2 so as to be maintained in contact with the cathode of battery 1 when the latter is disposed therein, and extends out of the battery casing. Lid 5 formed of a metal material such as brass is adapted to close the battery receiving chamber, and when it is closed in place, it contacts the anode of battery 1 to serve as the other conductive terminal member which represents the ground connection terminal. Lid 5 is formed with threads 5a which engage female threads 6 formed in inward projection 6 from an outer panel of a photographic camera. To limit the extent of movement of lid 5 beyond projection 6, the latter is formed with step 6b, which is engaged by a flange portion of lid 5. In this manner, the anode of battery 1 is electrically connected with panel 6 through lid 5. Washer 9 with a tongue is mounted inside panel 6 by means of set screw 8, and lead wire 10 is soldered to the tongue for an electrical interconnection. It is to be noted that terminal member 4 is also soldered with lead wire 7 for connection with an electrical circuit. In this manner, the panel 6 of the camera serves as an electrical conductive path. It will be appreciated that since lid 5 is detachably mounted on panel 6, it is necessary that panel 6 and lid 5 be both formed of a metal material such as brass and machined by drawing, deburring and tapping. This resulted in an increased cost of the battery casing and hence the overall assembly in which it is used.
It is then desirable to eliminate such disadvantages by forming lid 5 and the body of the casing including panel 6 of an inexpensive material such as plastics which may be easily machined. However, in the prior art arrangement, lid 5 is used as a terminal associated with one electrode of the battery and panel 6 used as a conductive path, so that these parts could not have been formed of a plastic material.